A. This procedure includes guidance on cleaning blackened
exterior copper. When copper weathers,
it naturally
develops a green-grey patina. Blackened
encrustations
may result from several things, including
contact with
chemicals, contact with incompatible
metals or air
pollution. The resulting stains
are generally not
harmful to the copper, though they may
be aesthetically
objectionable.

B. See 01100-07-S for general project guidelines
to be
reviewed along with this procedure.
These guidelines
cover the following sections:

1. Safety Precautions

2. Historic Structures Precautions

3. Submittals

4. Quality Assurance

5. Delivery, Storage and Handling

6. Project/Site Conditions

7. Sequencing and Scheduling

8. General Protection (Surface
and Surrounding)

These guidelines should be reviewed
prior to performing
this procedure and should be followed,
when applicable,
along with recommendations from the
Regional Historic
Preservation Officer (RHPO).

C. For additional information on the characteristics,
uses
and problems associated with copper,
see 05015-01-S.

PART 2---PRODUCTS

2.01 MATERIALS

NOTE: Chemical products are sometimes sold under a
common
name. This usually means that the substance is not
as pure as
the same chemical sold under its chemical name. The
grade of
purity of common name substances, however, is usually adequate
for stain removal work, and these products should be purchased
when available, as they tend to be less expensive. Common
names are indicated below by an asterisk (*).

A. Phosphoric Acid:

1. A syrupy or deliquescent tribasic
acid used
especially in preparing
phosphates (as for
fertilizers), in rust-proofing
metals, and as a
flavoring in soft drinks.

2. Other chemical or common names
include
Metaphosphoric acid;
Orthophosphoric acid;
Phrophosphoric acid.

NOTE: TEST CLEAN A SMALL INCONSPICUOUS AREA BEFORE
ATTEMPTING
TO CLEAN LARGE AREAS.

NOTE: WHEN CLEANING LARGE SURFACE AREAS, EMPLOY THE
USE OF
PROFESSIONAL HELP.

A. Mix 6 parts concentrated phosphoric acid with
1 part
concentrated nitric acid, diluted at
least 50% with clean
potable water. The mixture should
have a pH between 1
and 1.5.

B. Apply the solution to the stained copper surface
using a
cellulose sponge mop or similar hand
applicator. Let the
solution sit for approximately 1 minute.

CAUTION: AVOID APPLYING CLEANING
SOLUTION TO METAL IN
DIRECT SUN, AS IT BECOMES VERY HOT,
AND THE DETERGENT OR
SOAP SOLUTION WILL DRY IN STREAKS BEFORE
IT IS POSSIBLE
TO RINSE IT OFF. THESE STREAKS
CAN VERY EASILY BECOME
PERMANENT AND CANNOT BE REMOVED WITHOUT
ABRASION.

C. Remove the solution by wiping the surface with
a sponge
soaked in sodium bicarbonate. Follow
this by wiping the
surface with a sponge soaked in ammonium
oxalate.

D. Thoroughly rinse the surface with clean, clear
water and
dry with clean, soft cloths. Repeat
the process as
required to achieve the desired level
of cleanliness.